The chromosomal arrangement, structure and developmentally regulated expression of rabbit globin genes will be studied. A large library of recombinant bacteriophage containing randomly generated fragments of rabbit genomic DNA has been screened to isolate sets of clones containing alpha-like and beta-like globin genes. A cluster of four linked beta-like globin genes has been extensively characterized, and the alpha-like globin genes will be mapped in the cloned genomic fragments. Any obvious additional globin genes will also be isolated and mapped. The developmental time course of gene expression will be established by analyzing globin RNA and protein at stages of increasing embryonic and fetal maturity. The size and internal structure of transcription unit will be determined for all the isolated genes. The transcription initiation point will be defined by analyzing the dose dependence of UV-induced transcription termination. The distribution of mRNA-coding and noncoding regions will be analyzed by visualizing hybrids of mRNA and DNA in the electron microscope and by mapping the DNA segments protected from a single-strand specific nuclease by mRNA. This latter assay provides a sensitive approach to answering whether globin gene control operates at transcription or RNA processing. These studies are required to understand the molecular basis for developmental regulation of gene expression.